Respiratory organs in molluscs.

The organs of the respiratory system of molluscs are located in the visceral mass. Not all molluscs live in water, some live on land. The gills help those who live in the water. Aquatic molluscs such as snails and octopuses usually breathe using gills inside their mantle. Pipes, called siphons, bring water from the body and back. Land snails and slugs do not have gills; they breathe using the mantle cavity, which has a large surface area lined with blood vessels. Diffusion occurs through the moist skin of the molluscs.